Objective To investigate the effect of combined spinal and epidural anesthesia (CSEA) with sufentanil in the subarachnoid space on fetal heart rate and its possible mechanism. Methods A total of parturients undergoing CSEA for labor analgesia were selected. According to the random number table method, they were divided into three groups (n=30): a sufentanil 8 µg group (S8 group), a sufentanil 5 µg group (S5 group) and a ropivacaine 3 mg group (R3 group). All the three groups were subject to CSEA. Parturients in the S8 group, the S5 group, and the R3 group were injected with 1 mg/L sufentanil at 0.8 ml, 1 mg/L sufentanil at 0.5 ml, or 1% ropivacaine at 0.3 ml diluted with cerebrospinal fluid to 1.5 ml in the subarachnoid space at a constant rate. The abnormal fetal heart rate and uterine contraction were recorded from the beginning of labor analgesia to 30 min after labor analgesia. Their Visual Analogue Scale (VAS) scores and levels of epinephrine, norepinephrine, oxytocin, and prostaglandin E2 (PGE2) were recorded before labor analgesia (T0), 5 min after labor analgesia (T1), 15 min after labor analgesia (T2) and 30 min after labor analgesia (T3). The incidences of complications such as hypotension, pruritus, conversion to cesarean section and neonatal 1 min, 5 min and 10 min Apgar score were recorded. Results There was no statistical difference in the incidences of abnormal fetal heart rate, hypotension, conversion to cesarean section, enhanced uterine contraction after labor analgesia among the three groups (all P>0.05). There were no statistical differences in the levels of epinephrine, norepinephrine, oxytocin, PGE2, and VAS scores at T0, T1, T2 and T3, and neonatal 1 min, 5 min and 10 min Apgar score among the three groups (all P>0.05). The incidence of pruritus after labor analgesia in the S8 and S5 groups was significantly higher than that in the R3 group (all P<0.05); the incidence of pruritus in the S8 group was higher than that of the S5 group, without statistical difference (P>0.05). Conclusions There is no statistical difference in the incidence of fetal heart rate abnormalities after CSEA with the administration of sufentanil 8 µg, 5 µg, or ropivacaine 3 mg into the subarachnoid space. The analgesic effect is satisfactory and can be safely used for labor analgesia.